leetcode-95-Unique-Binary-Search-Trees-II

发表于   |  

描述

Given n, generate all structurally unique BST’s (binary search trees) that store values 1…n.

For example,
Given n = 3, your program should return all 5 unique BST’s shown below.

分析

上一题是leetcode-96-Unique-Binary-Search-Trees，只需要得到个数，而这道题是把所有的二叉搜索树都输出。

解决方案1(C++)

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<TreeNode*> generateTrees(int n) {
        vector<TreeNode *> result;
        if(n == 0) {
            return result;
        }
        return generate(1, n);
    }
private:
    vector<TreeNode*> generate(int start, int end) {
        vector<TreeNode *> result;
        if(start > end) {
            result.push_back(NULL);
            return result;
        }
        for(int k = start; k <= end; k++) {
            vector<TreeNode *> left = generate(start, k-1);
            vector<TreeNode *> right = generate(k+1, end);
            
            for(auto i: left) {
                for(auto j: right) {
                    TreeNode *node = new TreeNode(k);
                    node->left = i;
                    node->right = j;
                    result.push_back(node);
                }
            }
        }
        return result;
    }
};

相关问题

题目来源